The invention relates to an apparatus on a spinning preparation machine, for example a flat card, roller card, draw frame, combing machine or the like, for ascertaining the mass and/or fluctuations in the mass of fibre material, for example at least one fibre sliver, fibre web or the like, of cotton, synthetic fibres or the like.
The invention relates to the contact pressure of a feeler device on a fibre bundle in a sliver guide means, such as is used for measuring the thickness of fibre bundles on a textile machine. Such a textile machine can be a flat card, a draw frame, a flyer or a combing machine. The contact pressure of the feeler device is important for the formation of a correct measurement signal relating to the thickness of the fibre bundle. The measurement signal relating to thickness is important for controlling other processes on the textile machine. In order to ascertain the thickness of a fibre bundle, the fibre bundle is guided over a sliver guide means that is installed in fixed position. Such a sliver guide means can be a feeler roller which is fixed with its rotational axis, or a rod, a sliver guide channel or a sliver funnel. The fibre bundle is in contact with the sliver guide means and is guided thereby. A feeler device is pressed onto the fibre bundle guided in the sliver guide means. The contact pressure is provided by a spring which is under tension and is connected to the feeler device. The feeler device is movably mounted, that is to say in dependence upon the thickness of the fibre bundle being conveyed the feeler device moves at a distance from the sliver guide means. In so doing the feeler device can perform a pivoting movement or a back and forth movement. The feeler device is arranged with a signal converter which detects the movement of the feeler device and converts it into an electrical measurement signal. The feeler device can be, for example, a movable feeler roller. The movable feeler roller is pressed onto the fixed feeler roller. The movable feeler roller can be arranged in a pivot arm or reciprocating carriage. A spring engages the pivot arm or the reciprocating carriage and provides the contact pressure. A feeler device is also to be understood as being a feeler element which, diagrammatically, may take the form of a finger. Such a feeler element projects towards the sliver guide means in the conveying direction. The portion of the feeler element that is in contact with the fibre bundle is in the form of a slide surface. The feeler element is movable vertically and at a right angle to the running direction of the fibre bundle. Because the feeler element is in the form of a lever arm, it is pressed by springs in the direction of a fixed slide surface of a sliver guide channel or of a sliver funnel. The sliver guide channel or sliver funnel corresponds to a sliver guide means. The thickness of the fibre bundle is ascertained by means of the movement of the feeler element. A connected signal converter converts the amount of movement into an equivalent electrical signal. The term “fibre material” is to be understood as meaning a fibre bundle such as a fibre web, a fibre sliver twisted from a plurality of slivers, a drafted fibre sliver or a fibre tuft web, a fibre tuft feed.
A known apparatus (DE 195 38 496 A) has a pair of feeler rollers, the spacing of one of the feeler rollers being variable relative to the other and its excursion relative to an inductively operating contactless displacement sensor being determined by means of a lever arm having a pivot joint. The output signal of the displacement sensor is transmitted by means of a signal converter, which may be a proportional element, to a measured value memory which is able to change the drive speed of the middle and inlet rollers of the drafting system by way of a desired value step. A disadvantage is that such displacement sensors are electrically connected to a shielded control line by way of a special inbuilt connector. On account of the anti-inductive protection, that is to say the protection against induction voltage or induction currents, the control line consists of a special-purpose line. In order to prevent any interference effects on the measurement signal, that line must be connected in accordance with EMC (electromagnetic compatibility) guidelines. It should also be borne in mind that the counter-element must consist of a metallic material and the sensor has a certain stray field. A further problem is that the sensor is temperature-dependent. In addition, the amount of space required for certain applications, in which small dimensions are a factor, is too large.
It is an aim of the invention to provide an apparatus of the kind described at the beginning which avoids or mitigates the said disadvantages, which is, especially, simple in terms of structure and installation and which allows improved and more accurate measurement of the fibre bundle.